The present invention broadly relates to a method of fabricating a thermally insulated body and, more specifically, pertains to a new and improved method for fabricating a thermally insulated body, e.g. a pipe, having an inner shell and an outer shell, particularly a metallic inner shell and a metallic outer shell.
The thermal insulation of bodies is principally undertaken for two reasons, either to inhibit the heat losses of a medium or to prevent a thermal loading or stressing, for example of the outer shell of a container. A vacuum is the ideal thermal insulation against heat transmission or conduction; a layer or film reflecting infrared rays is suitable against heat radiation.
A thermally insulated body is known from the European Pat. No. 17,095, published Oct. 10, 1980, which comprises an outer shell and an inner shell. The intermediate space formed between both shells is maintained under vacuum and is filled with powdered porous material, e.g. activated charcoal or siliceous earth. This body is fabricated by first filling the intermediate space with the powdered insulating material and thereafter evacuating and then sealing. This procedure is particularly slow, since both the gas filling the intermediate space and the gas contained in the porous particles must be evacuated.
In order to avoid these disadvantages, the German Patent Publication No. 2,750,457, published June 22, 1978, proposes employing a gas with low thermal conductivity in place of the vacuum, which simultaneously produces the advantage that no long-term diminution of the thermal properties occurs.
A thermally insulated pipe is described in the German Patent Publication No. 2,333,933, published Jan. 24, 1974, which, among other things, comprises an inner shell and an outer shell forming an intermediate space which is filled with expanded perlite. A vacuum is obtained in the intermediate space by filling the intermediate space with carbon dioxide and relying on the temperature of the medium stored or transported in the insulated body, which is below the condensation temperature of carbon dioxide, to condense the carbon dioxide and in this manner generate a vacuum in the intermediate space. Such a thermally insulated body can, however, only function when the medium has a suitable temperature.